Click the link to read the article on the National Drought Mitigation website (Leah Campbell):
This summer has been one for the books with heat and rainfall records toppling around the U.S. The country experienced several “1-in-1,000” storm events in the span of just a few months, leading to devastating flooding from Kentucky to Montana. Mississippi had its wettest August on record. Nebraska had its second driest. Nineteen states had Julys that were amongst their 10 hottest in terms of average temperature, including Texas, which had its warmest July going back more than 100 years.
Drought records have also been made and broken in the last few months. In mid-September, Puerto Rico broke a streak of 91 consecutive weeks of drought when Hurricane Fiona dumped over 30 inches of rain in some places. At the end of August, over 90% of Hawaii was in drought for the first time, which continued for four weeks.
The country as a whole recently hit another sobering record: more than two years with over 40% of the contiguous U.S. in moderate drought or worse, what the U.S. Drought Monitor classifies as D1 or above. As of the latest USDM map on Oct. 4, it’s been 106 straight weeks. The last time the extent of drought in the Lower 48 dipped below 40% was on Sept. 29, 2020 (when it was a close 39.7%).
The current streak of widespread drought marks the longest such streak since the USDM began in 2000. The second longest streak, from June 2012 to October 2013, was only 68 weeks. After that is a 65-week stretch from March 2002 to June 2003. Both of those earlier periods are recognized as some of the most severe droughts on record in the U.S.
According to Brad Rippey, a meteorologist with the U.S. Department of Agriculture, the percentile ranking methodology of the USDM — where moderate drought is classified as a once per 5- to 10-year occurrence — would suggest that, statistically, drought coverage should be closer to 20% this time of year. Instead, as of the Oct. 4 map, nearly 53% of the contiguous U.S. and over 44% of the entire country and its territories, was in D1 or worse condition.
“I’ve been involved with the Drought Monitor since the beginning and have seen a lot of U.S. droughts come and go,” said Rippey. “The drought of 2020-2022 really stands out for its longevity. In 2012-2013, we were done with the worst of it in a little over a year.”
Rippey ascribes the longevity and extent of the current drought in part to back-to-back-to-back La Niña events. That “triple dip,” as Rippey calls it, has happened only two other times in the modern record, first in the mid-1970s and then the late 1990s.
La Niña and its counterpart El Niño are periodic global phenomena related to sea surface temperatures. During La Niña, the Pacific Ocean along the South American coast is cooler than normal near the equator. Meanwhile, warmer surface water is driven across the Pacific toward Asia. The movement of all that heat has significant and complex impacts on weather across the planet.
“In a general sense, when it comes to the U.S., La Niña is a drought-maker, while El Niño is a drought-breaker,” said Rippey. The current and ongoing La Niña, he explains, developed during the second half of 2020 and has generally persisted since then. The National Oceanic and Atmospheric Administration predicts that La Niña is likely to continue in the Northern Hemisphere through the end of the year at least.
Long-lasting, Extensive and Extreme
The current drought, though, isn’t just noteworthy for how long it’s lasted. It’s also been particularly widespread, fast-emerging and intense. Coverage peaked for the summer on July 12 with just shy of 45% of the entire U.S. and Puerto Rico in drought. For the contiguous U.S., it peaked closer to 52% a few weeks later. For three weeks through mid-August, in fact, 44 states across the country were at least partially in drought. Only Ohio hasn’t recorded any drought thus far this year.
(Looking at the year as a whole, drought coverage peaked back in early March at 51% and 61% for the entire U.S. and the contiguous U.S., respectively. In both cases, that’s just a few percentage points shy of the USDM record set during the 2012-2013 drought.)
In terms of speed, several states in the Southern Plains this summer had to confront what’s called “flash drought.” Through July, Arkansas, Missouri and Oklahoma all experienced a one-category-per-week degradation in drought conditions, what Brian Fuchs, a Drought Monitor author and climatologist at the National Drought Mitigation Center, says is “lightning speed by the standards of drought.” While drought tends to be a slow-onset crisis, intense heat can contribute to faster-emerging dry conditions. Indeed, Oklahoma experienced its fifth hottest July on record this year, in terms of average temperature, and Arkansas its seventh.
In Arkansas, drought coverage was not even 2% at the end of June. Just four weeks later, 89% of the state was in drought, and over a fifth was in extreme drought or D3 according to the USDM. Though conditions then began to improve, back to less than half the state in drought less than two months later, conditions degraded again in the second half of September.
These kinds of rapid changes can create significant hardship for communities and for livestock and agricultural producers. That concern is evident in the number of observations submitted to CMOR, the NDMC’s database of crowdsourced, geo-located conditions reports. As of the end of September, over 3,300 observations have been submitted to CMOR this year. Over 1,300 were from July alone, from just the three states most affected by the flash drought. In comparison, only 1,200 observations were submitted to CMOR for all of 2019 from across the whole country.
Rapid changes can also cause headaches for Drought Monitor authors trying to make sense of different environmental datasets.
“One of the most challenging things this summer from a drought monitoring perspective has been keeping up with the different time scales drought has been occurring in different places,” said Curtis Riganti, a climatologist with the NDMC and a Drought Monitor author.
Riganti explains that they’ve been getting a lot of “mixed signals” this summer. “In the Southern Plains, there’s been flash drought over relatively wet conditions earlier in the year,” said Riganti. “In the Southwest, we’ve had the opposite problem, and it’s been a challenge to balance long-term groundwater, precipitation and reservoir deficits with the fact that it’s been a wet summer.”
With an active North American Monsoon season, drought signals in the Southwest have been particularly complex. Nevada had its third wettest August on record, and Aug. 5 was the wettest day ever in Death Valley, California, which received about three quarters of its annual rainfall in a matter of hours. Yet, years of severe drought across the region mean that water supplies are still concerningly low. On the Utah-Arizona border, for example, Lake Powell is only 25% full as of the end of September, with water levels down 16 feet from last year.
Unrelenting Heat and Hardship
Part of why drought was so intense and extensive this summer, and so difficult to deal with, was that temperatures have been sweltering in many places these last few months. Nationally, this summer was the third hottest June-August period on record, and, at the state level, several heat records were broken.
This June was the tenth hottest June on record. July was even worse. It was the third hottest July on record nationally, and almost every Western state hit top-10 records for heat for the month. The Southeast and the Midwest got some relief in August, but it was unrelenting elsewhere. Eight states in the Northeast and the Northwest all recorded their hottest August on record. In California, which had its second-hottest August, an extreme heat wave gripped the state at the end of the month, with several cities breaking records (on Sept. 5, Livermore, California hit 116 degrees, setting an all-time record for the Bay Area).
This kind of extreme heat not only drives drought, but also exacerbates its various impacts, making dry conditions more challenging. As of the latest USDM map on Oct. 4, over 126 million people across the U.S. were affected by drought. For just the contiguous U.S., the number affected was over 125 million, almost 40% of the entire population of the Lower 48.
From the start of the year, through the end of September, the NDMC added more than 3,300 records to the Drought Impact Reporter, the center’s database of drought impacts. Each record represents a county, city or state confronting a specific challenge related to drought and dry conditions, from water restrictions and burn bans to low water levels, losses of recreation and algae blooms. Combined with the summer’s soaring inflation and rising costs for irrigation water, fuel and livestock feed, it’s been a particularly hard year for agricultural producers who have had to confront crop losses, reduced yields and insect infestations.
“Clearly something is happening to U.S. and global weather and climate patterns before our very eyes,” said Rippey. “It’s a very exciting time, but also a scary time to be a meteorologist. We may not know exactly what will happen, but all evidence says we can expect more extremes, including drought, going forward.”